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Abstract
Background: The purpose of this study was to measure blood flow in the carotid and femoral
arteries, heart rate and blood pressure in response to postural challenge in older adults. A second
purpose was to determine if older men and women have different cardiovascular responses to a
postural challenge such as tilt.
Methods: Thirty-seven healthy elderly men and women participated in this study (69-82 years
old). All subjects had similar physical activity levels. Postural challenge was induced by a 600 tilt at
the level of the waist. Continuous carotid blood flow and femoral blood flow was measured with
Doppler ultrasound.
Results: Carotid blood flow was significantly reduced 17% in both men and women immediately
after tilt (p < 0.00 1), and by 3.2% two minutes after tilt (p < 0.001). Femoral blood flow decreased
59.4% in men and 61% in women immediately after tilt (p < 0.001), and remained significantly
decreased two minutes after tilt by 21 % (p <0.001). Heart rate increased by 15% in men (p < 0.001),
and 26% in women immediately after the tilt (p < 0.001). Heart rate returned to resting values
within two minutes in both men and women. Response to tilt was not significantly related to self-
report physical activity levels or to six-minute walk time.
Conclusion: A postural challenge induced larger changes in the femoral artery compared to the
carotid artery. There were no differences between men and women to a tilt table test except for
differences in heart rate response. There was no difference in the blood flow responses to postural
challenge with physical activity level or between healthy older men and women.

Background
Changes in body position invoke large changes in hydro-
static pressure, which induce large changes in blood vol-
ume within the body [1]. The cardiovascular system in
healthy individuals has the ability to rapidly respond to
such 'postural challenges'. Detection of abnormal cardio-

vascular responses to postural challenge has been pro-
posed as an early sign of cardiovascular disease. Tilt tests,
either of the whole body or only above the waist, have
been used to study the cardiovascular response to changes
in blood volume [2-4]. Most studies that have used tilt
tests report the responses after two minutes when heart

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rate and blood pressure have stabilized. Few studies, how-
ever, have evaluated the immediate cardiovascular
response to tilt, which is important as the immediate
responses are larger in magnitude than the stabilized
responses, and may be more sensitive to changes in cardi-
ovascular function [4-7].

While heart rate and blood pressure changes are routinely
measured in response to postural challenge, actual
changes in arterial blood flow have been less well studied.
Approximately 75% of the blood flow to the brain comes
from the common carotid arteries, thus, regulation of
flow immediately after a postural challenge is highly reg-
ulated and very important to maintain function [8]. How-
ever, changes in the femoral artery might be expected to be
just the opposite, with large changes in blood flow to
assist in maintaining blood flow to the brain.

Aging and cardiovascular disease can impair the speed
and response of the cardiovascular system to postural
challenge [4,9,10]. Gender may also influence vascular
kinetics. Gender differences have been found in body
weight, heart rate, stroke volume, and arterial compliance.
For example, men have larger carotid arteries, and intima-
media thickness and wall stress of large arteries affecting
blood flow are generally larger in men [11,12]. However,
fluctuations in estrogen hormone levels in women affect
arterial distensibility [13]. In addition, arterial stiffness,
which has also been shown to be modulated by sex hor-
mones, may affect blood flow velocity in conduit arteries
[13]. These differences between men and women may
affect systolic and diastolic blood pressure [12] as well as
the ability to withstand cardiac events and respond to
orthostatic stress [14,15]. Since gender may have a pro-
found influence on the risk of cardiovascular disease and
death, it is important to understand the effects of healthy
aging and gender on autonomic control of the cardiovas-
cular function [14].

The purpose of this study was to measure the immediate
response of carotid and femoral artery blood flow, heart
rate and blood pressure responses to postural challenge in
older adults. A second purpose was to determine if there
were gender differences in heart rate, blood pressure, or
blood flow responses after a tilt in elderly individuals, and
if levels of physical activity correlate with cardiovascular
responses to tilt.

Methods
Subjects
Thirty-seven subjects between the ages of 69 and 82 years
volunteered to participate in the study. Nineteen subjects
were male and eighteen subjects were female. All subjects
had similar physical activity levels. All subjects reported
being Caucasian except for one African-American female.

The subjects reported to the laboratory after eating a low
fat meal, and did not take any medications the morning
of the test. Eleven out of thirty-seven subjects took high
blood pressure medication regularly, but did not take it
the morning of the test. Only one subject was a smoker
and eleven more reported being ex-smokers. Subjects were
excluded from the study if they had a pacemaker, suffered
from severe back pain, were under alpha-blocker medica-
tion or were diagnosed with heart disease six months prior
to participating in the study. The study was conducted
with the approval of the Institutional Review Board at the
University of Georgia and written informed consent was
obtained from all participants.

Protocol
The study included one testing session between 8:00-
11:00 am in a quiet, comfortable room (temperature 20-
22 C). The subjects rested for at least 10 minutes to allow
stabilization, and then the testing procedure proceeded as
follows.

Postural Challenge Test
The subjects were placed in a supine position for 5 min-
utes prior to testing. Baseline measurements were
obtained for blood flow, heart rate, and blood pressure
during 5 minutes of quiet rest. The tilt response was pro-
duced by manually lifting a hinged table 60 degrees in
1.5-2 seconds. Subjects were placed so that the hinge of
the table corresponded to their waist. Subjects were not
aware of when the tilt procedure was to be conducted.
Once tilted, the subject was maintained in the upright
position for 2 minutes while all measurements were being
collected. The subject was then placed back in the supine
position for at least 5 minutes or until all measurements
stabilized, whichever was shorter. When all parameters
stabilized, the tilt was repeated. The order of carotid and
femoral artery blood flow measurements were alternated
for different subjects throughout the whole experiment.
Data for reproducibility was collected using several tilts to
determine baseline measurements and the magnitude of
change to tilt. Previous data collected in our laboratory
suggested high levels of reproducibility of carotid and
femoral measurements (>95%) and no evidence of an
order effect in repeated tilts (p > 0.05). Further, others
have reported high reproducibility and sensitivity during
heap-up tilt testing or blood flow testing using this tech-
nique [16,17].

Vascular Measurements
Blood flow measurements of the right common carotid
and femoral arteries were measured continuously by use
of a quantitative Doppler Ultrasound (LOGIQ 400 CL,
General Electric) [18]. A linear array transducer was used
with frequencies of 6-9 MHz. The imaging sites were
located 2-3 centimeters proximal to the carotid

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Table I: Subject Characteristics

http://www.dynamic-med.com/content/3/1/1

Age (yrs)
Height (cm)
Weight (kg)
BMI (Kg/m2)
Six-Minute Walk (m)

Men (n = 18)

75.1 4.2
174.6 7.3
81.9 11.5
26.9 3.0
589 83

bifurcation in the right common carotid artery, and on the
upper third of the thigh in the right superficial femoral
artery. Diameters were measured in the axial view during
diastole and B mode images were saved to magnetic opti-
cal disk for analysis. Images were later analyzed to deter-
mine vessel size. Pulsed Doppler ultrasound was recorded
in the longitudinal view using an insonation angle
between 50 60. The velocity gate was set to include
the entire arterial diameter. Time average maximum
blood velocity (TAMAX) was measured for each cardiac
cycle and recorded throughout the experiment. Blood
flow was calculated as the product of vessel cross sectional
area and the TAMAX. All subjects had ankle-brachial
indexes (ratio ofbrachial artery systolic pressure over pos-
terior tibial systolic pressure) determined after the pos-
tural challenge.

Physical Fitness and Physical Activity
The subjects performed a six-minute walk test in a quiet
corridor to assess their levels of physical fitness. The sub-
jects walked back and forth in a 50-meter corridor for six
minutes at their own pace, and distance walked was calcu-
lated. Self-reported physical activity over the previous 30
days was recorded using the Yale Physical Activity Survey
[19]. Activity was quantified by kilocalories and frequency
of physical activity. Both measures, the six-minute walk
and the Yale physical activity survey, were used to measure
any correlations between physical activity and the cardio-
vascular responses to tilt.

Statistical Analysis
An independent t test was applied to determine if there
were any differences between men and women on heart
rate, blood pressure, or blood flow immediately or 2 min-
utes after tilt. A paired t-test was used to determine if there
were any significant changes before and after tilt. Pearson
product moment correlations were conducted to deter-

Women (n = 17)

74.9 4.1
161.4 6.2
70.9 10.5
27.3 5.0
490 86

P value

0.876
0.001*
0.005*
0.732
0.001*

mine relationships between variables. The level of signifi-
cance was set at 0.05 for all statistical analyses and results
were expressed as means standard deviation.

Results
Subject Demographics
The physical characteristics and physical fitness of the sub-
jects are shown in Table 1. There were no differences in
age or health status between the older male and female
subjects. The ankle brachial index for the tested leg aver-
aged 1.28 (range of 0.91-1.72). There were no statistical
difference in carotid arterial diameter between men and
women (6.87 0.75 mm for men, 6.48 0.57 mm for
women, p = 0.09). Men did have larger femoral artery
diameters than the women (7.05 1.03 mm for men, 5.66
0.88 mm for women, p < 0.001).

Carotid Blood Flow Responses to Tilt
Men and women had similar carotid artery blood veloci-
ties but men had significantly higher carotid blood flows
(p < 0.05). In response to tilt, blood flow initially
decreased and then returned to normal (Figure 1). There
were no significant differences between men and women
immediately after tilt (p = 0.429) or after 2 minutes (p =
0.204). When men and women were combined, carotid
blood flow decreased by 17% immediately after tilt (p <
0.001) and remained 3.2% below initial values two min-
utes after tilt (p < 0.001). The average time for carotid
blood flow to decrease to a minimum value after tilt was
25.4 13.7 seconds (Figure 2). Carotid diameter did not
change throughout the 2 minute tilt test (p > 0.05).

Femoral Blood Flow Responses to Tilt
Women had significantly higher blood velocities at all
time points (p < 0.05) but similar blood flow values
(again due to the men having larger femoral artery diam-
eters). In response to tilt, femoral artery blood flow
decreased initially and remained reduced after two min-
utes (Figure 3). The initial decrease in femoral artery
blood velocity was similar between the men (59%) and
women (61%) immediately after tilt and after two
minutes (21% for both men and women). With men and
women combined the decrease in femoral artery blood

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to-
1.0-
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0.8-
0.7-
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0.5-
0.4-
0.3-
0.2-
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0.0"

Carotid

a.

-60

120

Time (s)
Figure I
Example of continuous blood velocity measurements in the carotid artery. Values are from a 71 year old female subject. Time
zero on the x-axis represents the time when the tilt was performed.

0.50
0.45
0.40
0.35
0.30
0.25
0.20
0.15
0.10
0.05
0.00

baseline

Lu

peak

Figure 2
Example of continuous blood velocity measurements in the carotid artery. Values are from a 71
zero on the x-axis represents the time when the tilt was performed.

0 women
E men

2 min

year old female subject. Time

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Dynamic Medicine 2004, 3

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0.35 -
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0.20
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0.10 -
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-60

Femoral

60

Time (s)

Figure 3
Example of continuous blood velocity measurements in the femoral artery.
zero on the x-axis represents the time when the tilt was performed.

flow was highly significant (p < 0.001). The average time
for femoral blood flow to decrease to a minimum value
after tilt was 37.6 + 21.5 seconds (Figure 4). Femoral
diameter did not change throughout the 2 minute tilt test
(p > 0.05).

Heart Rate and Blood Pressure Responses to Tilt
Heart rate increased by 15% in men (p < 0.001) and 26%
in women (p < 0.001) immediately after the tilt. Women
exhibited a significantly greater heart rate response than
men immediately after tilt (p = 0.045). Heart rate returned
to the initial pre-tilt values within two minutes in both
men and women. Systolic and diastolic blood pressure
responses immediately and after two minutes were similar
in males and females. Thus, the blood pressure data was
grouped together for the men and women for further anal-
yses. Systolic blood pressure was significantly reduced by
25% immediately after tilt (p < 0.001), and by 5% after
two minutes of tilt (p = 0.017). Diastolic blood pressure
was significantly reduced by 14% after tilt (p < 0.001) but
returned to resting values after two minutes (p = 0.087).

Physical Activity
The average walking distance was 541 meters (range of
320 to 778 meters). Self-reported physical activity aver-
aged 4732 kcal/week (ranged of 1692 to 8892 kcal/week).
Frequency of vigorous physical activity averaged 62 min-
utes/week (range of 27 to 103 minutes). There were no
differences in self-reported physical activity between
males and females. There were no significant correlations
between physical capacity as measured by 6 minute walk
time, blood flow, heart rate, or blood pressure responses
to tilt. This was true for both men and women. Similarly,
there were no significant correlations between the
responses to tilt and physical activity levels as measured
by kilocalories per week or the number of daily activities
(Yale physical activity survey).

Discussion
The main finding of this study was that both carotid and
femoral artery blood velocities decreased in response to
postural challenge in healthy older adults, with the imme-
diate responses being much greater than the two minute
response. Immediate carotid and femoral blood flow
responses upon tilt have not been studied well [16]. We
found that blood flow reached minimum values approxi-
mately 30 seconds after tilt. However, there was a high
degree of variability in the time to reach minimum values
and more accurate measurements to determine the time
course of changes may be useful. Our responses in the
carotid artery after two minutes [20,21] and in the femo-
ral artery after 1 or 2 minutes [22,23] are similar to those
reported in previous studies. Femoral artery blood flow
showed significantly larger changes after tilt than the
carotid artery.

There were no gender-related differences in blood flow
responses to postural challenge. However, some gender
differences were seen in blood velocity and artery diame-
ter. Men had larger femoral arteries and women had
higher femoral blood velocities compared to the men.
There was also a tendency for men to have larger carotid
arteries as reported previously [11,12], although this
finding was not significant. Nevertheless, the relative
changes in blood velocity and blood flow were similar
between men and women in both the carotid and femoral
arteries. The lack of gender differences in blood flow
response to tilt was unexpected, as previous studies have
reported gender differences in response to tilt heart rate,
blood pressure, and in sympathetic nerve activity [22,24].
Females had a greater increase in heart rate than males
immediately upon tilt. This response is consistent with lit-
erature in which females show higher resting heart rates
than males [2], and larger increases in heart rate due to a
postural stress [2,12,25-28]. Reports by Imadojemu et al.
[22] and Morgan et al. [23] also chose to combine their
male and female subjects in their presentation of blood
flow responses to tilt, supporting our lack of gender differ-
ences in blood flow.

Consistent with previous studies, we found that tilt pro-
duced transient increases in heart rate [2,12,26-29]. The
changes in heart rate in our study were lower than some
previously reported literature and may be due to a tilt
from the waist only [4,29]. We chose to use a passive tilt
test from the waist only to allow measurement of femoral
artery blood flow and to minimize the chance of subjects
having syncope. Previous studies have shown that whole
body tilt tests in frail older subjects can produce syncope
in up to 50% of the cases. However, in our study of rela-
tively healthy older adults using only waist tilt, no subjects
reported any symptoms of syncope. In addition, there are
no reports in the literature investigating immediate
responses of blood flow to tilt. This is probably due to the
challenging nature of the measurements since this test
includes a dynamic measurement of the carotid and fem-
oral arteries. Kojo et al. [16] studied healthy young sub-
jects and pediatric patients suffering from syncope by
measuring carotid blood flow after a 60 degree tilt. Most
of these young patients (50% of young healthy and 88%
of syncopal pediatric patients) also experienced signifi-
cant decreases in carotid blood flow due to tilt. However,
their measurements were collected every minute after tilt
during 20 minutes, and did not study the rapid changes of
carotid blood flow immediately after tilt in this popula-
tion [16]. Thus, our study reports measurements in an
area that has not been explored extensively, and provides
novel results in carotid and femoral blood flow immedi-
ately (within seconds) after a 60 degree tilt.

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We did not find any associations between physical activity
levels or walking distance and the responses to tilt. This
was despite finding a large range of fitness levels and activ-
ity histories, and using both self-reported activity levels
and directly measured walking distances (timed 6 minute
walk test). A previous study using the cardiovascular
response to a hand cold pressor test suggested that fitness
level was inversely related to changes in systolic blood
pressure but not to total peripheral vascular resistance
[30]. However, this study also found that fitness levels
were unrelated to changes in total peripheral vascular
resistance in response to the cold pressor test.

Conclusions
In summary, a 60 o tilt at the waist produced large changes
in carotid and femoral blood flow, heart rate, systolic and
diastolic blood pressure. Larger blood flow changes
occurred immediately after tilt compared to two minutes
after tilt. There were no differences between men and
women to a tilt table test except for differences in heart
rate response. Tilt at the waist did not produce syncope in
any older adults participating in this study, which is com-
mon problem in this population if whole body tilt is used.
Thus, this study demonstrated that immediate blood flow
responses after a modified tilt table test are attainable.
This method could prove to be a useful tool for determin-
ing cardiovascular disease risk with further research and
development. Another interesting observation is that
since we only acquired information on the common
carotid artery blood flow, the results may be blunted due
to the nature of this artery, where the blood is carried to
various regions of the head (e.g. eye, brain). Perhaps the
monitoring of the internal carotid artery alone would pro-
vide even more valid information on how blood flow to
the brain is affected during a postural stress such as tilt.

List of abbreviations
TAMAX Time average maximum velocity

Author's contributions
VC participated in the study design and data collection,
coordinated the study, carried out the statistical analysis,
and drafted the manuscript. JO coordinated the study and
data collection, carried out the statistical analysis, and
drafted the manuscript. LS participated in data collection
and coordination of the study. CB participated in data col-
lection and coordination of the study. KM participated in
the study design, coordinated the study, carried out the
statistical analysis, and drafted the manuscript. All
authors read and approved the final manuscript.

Acknowledgements
We would like to thank all the volunteers that participated in this study.
Financial support provided by NIH grant HL65179

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